Vertical heat transfer in the lower atmosphere over the Arctic Ocean during clear-sky periods

A diagnostic study of heat transfer within the lower atmosphere and between the atmosphere and the surface of the Arctic Ocean snow/ice pack during clear-sky conditions is conducted using data from the Surface Heat Budget of the Arctic Ocean (SHEBA) field experiment. Surface heat budgets computed for four cloudy and four clear periods show that, while the net turbulent heat fluxes at the surface are small during the cloudy periods, during the clear-sky periods they are a considerable source of surface heating, balancing significant portions of the conductive heat fluxes from within the snow/ice pack. Analysis of the dynamics and thermodynamics of the lower atmosphere during the clear-sky periods reveals that a considerable portion of the heat lost to the surface by turbulent heat fluxes is balanced by locally strong heating near the atmospheric boundary-layer (ABL) top due to the interaction of subsiding motions with the strong overlying temperature inversions surmounting the ABL. This heat is then entrained into the ABL and transported to the surface by turbulent mixing, maintained by a combination of vertical wind shear and wave-turbulence interactions. The frequency of stable, clear-sky periods, particularly during the winter, combined with these results, suggests that the downward transfer of heat through the lower atmosphere and into the surface represents an important component of the heat budgets of the lower atmosphere and snow/ice pack over the annual cycle.